Process for producing gasoline blending stock of high antiknock value

ABSTRACT

A COMBINATION PROCESS ID DISCOLSED FOR PRODUCING GASOLINE BLENDING STOCK HAVING F-1 CLEAR OCTANE NUMBER ABOVE 100 FROM NAPHTHA CONTAINING NORMAL PARAFFINS AND BRANCHED PARAFFINS INCLUDING SINGLY BRANCED PARAFFINS OF THE C6-C9 RANGE, WHICH COMPRISES FIRST DENORMALIZING (I.E., REDUCING THE STRAINGTH CHAIN HYDROCARBON CONTENT OF) THE NAPHTHA, HYDROFORMING THE DENRMALIZED NAPHTHA VIA A PLATINUM-CONTAINING CATALYST UNDER CONDITIONS YIELDING A C5+ REFORMATE WITH F-1 CLEAR OCTANE NUMBER OF AT LEAST 96, AND THEN DENORMALIZING THE REFORMATE. THE RESULTING REFORMATE PRODUCT NOT ONLY IS SUBSTANTIALLY FREE OF STRAIGHT CHAIN HYDROCARBONS BUT ALSO, DUE TO THIS SEQUENCE OF PROCESSING, HAS AN UNUSUALLY LOW CONTENT OF SINGLY BRANCHED PARAFFINS OF THE C6-C9 RANGE, WIHC COMPONENTS HAVE POOR OCTANE VALUES. PREFERABLY THE TWO DENORMALIZATION STEPS ARE EFFECTED BY MOLECULAR SIEVE ADSORBENTS. STRAIGNT CHAIN HYDROCARBONS DESORBED FROM THE ADSOBENT IN THESE STEPS MAY BE DEHYDROCYCLIZED TO INCREASE THE YIELD OF HIGH OCTANE GASOLINE BLENDING STOCK.

March 1973 A. J. GLESSNER ETAL 3,723,293

PROCESS FOR PRODUCING GASOLINE BLENDING STOCK OF 4 HIGH ANTIKNOCK VALUE Filed NOV. 1971 I 3 Sheets-Sheet 1 FEED FIGURE 1 NAPHTHA I V ,lo

DENORMALIZATION STEP 7 DENORMALIZED IW' NAPHTHA HYDROFORMING STEP USING PI-CONTAINING CATALYST AT 750' 975 F ZOO'TOO PSIG REFORMATE OF 96" OCTANE N0.

I2 DENORMALIZATION STEP n-PARAFFINS DEHYDROCYCLIZATION STEP ,1; GASOLINE BLENDING STOCK OF loo OCTANE NO.

INVENTORS ALFRED J. GLESSNER WILLIAM WAYNE WENTZHEIMER ATTORNEY Mam}! 1973 A. .1. GLESSN-ER ETAL 3,723,293

PROCESS FOR PRODUCING GASOLINE BLENDING STOCK OF HIGH ANTIKNOCK VALUE Filed Nov..l8, 1971 3 Sheets-Sheet 3 FIGURE 3 YIELD-OCTANE NUMBER RELATIONSHIP YIELD, VOLUME C GASOLINE PRODUCT 7o \{PROCEDUREC \(PROCEDURE A 68 as A m I02 I04 I06 I08 no RESEARCH (F-l) CLEAR OCTANE NUMBER INVENTORS ALFRED J. GLESSNER WILLIAM WAYNE WENTZHEIMER RENE F. KRESS BY M EQM AT ORNEY United States Patent O 3,723,293 PROCESS FOR PRODUCING GASOLINE BLEND- ING STOCK OF HIGH ANTIKNOCK VALUE Alfred J. Glessner, Glenolden, Pa., William Wayne Wentzheimer, Edgewood, Md, and Ren F. Kress, Media, Pa, assignors to Sun Oil Company of Pennsylvania, Philadelphia, Pa. Continuation-impart of application Ser. No. 112,140, Feb. 3, 1971. This application Nov. 18, 1971, Ser. No. 200,061

Int. Cl. C10g 35/08 US. Cl. 20885 14 Claims ABSTRACT OF THE DISCLOSURE A combination process is disclosed for producing gasoline blending stock having F-l clear octane number above 100 from naphtha containing normal parafi'ins and branched paraffins including singly branched paraffins of the C C, range, which comprises first denormalizing (i.e., reducing the straight chain hydrocarbon content of) the naphtha, hydroforming the denormalized naphtha via a platinum-containing catalyst under conditions yielding a C reformate with F-1 clear octane number of at least 96, and then denormalizing the reformate. The resulting reformate product not only is substantially free of straight chain hydrocarbons but also, due to this sequence of processing, has an unusually low content of singly branched parafiins of the C -C range, which components have poor octane values. Preferably the two denormalization steps are effected by molecular sieve adsorbents. Straight chain hydrocarbons desorbed from the adsorbent in these steps may be dehydrocyclized to increase the yield of high octane gasoline blending stock.

CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of Ser. No. 112,140, filed Feb. 3, 1971, now abandoned.

BACKGROUND OF THE INVENTION This invention pertains to a novel combination reforming process for converting low octane hydrocarbons to high octane gasoline components at high liquid yields.

It is common knowledge that automobile emission standards will become more stringent than present limits. Changes in engines, exhaust systems and fuel compositions will be necessary to meet these restrictions. For some time lead antiknock additive compounds in gasoline have been under attack as a health hazard. Proposed emission standards may require the use of a highly efficient converter or afterburner in the exhaust system. However, lead poisons the catalysts proposed for use in these catalytic converters. In light of this situation, fuel compositions may be altered so as not to contain any lead antiknock additive compounds or so as to be at a much lower concentration than is presently used. Replacing the octane values lost by the removal of lead requires costly and specialized processes such as catalytic reforming processes to produce high octane value components.

These processes involve the vapor phase treatment of naphtha fractions by contact with a catalyst such as a platinum-containing catalyst, a chromia-alumina catalyst, a molybdena-alumina catalyst or the like. The reforming process is usually carried out in a series of reactors operating under selected reforming conditions. During the treatment, various reactions take place, substantially simultaneously, or at various stages of the reforming process. For example, in a catalytic reforming operation employing a platinum-containing catalyst in contact with a naphtha fraction containing aromatics, naphthenes, isoparaffins and normal parafiins, dehydrogenation of the ice naphthenes to aromatics occurs while isomerization, hydrocracking and aromatization or dehydrocyclization of the parafiinic hydrocarbons take place. The cracking reaction is undersirable as it results in gas formation (C and lighter) and deposition of carbon on the catalyst, thereby reducing the yield of normal liquid products and causing deactivation of the catalyst. Nevertheless, in conventional practice it is usually necessary to employ reforming conditions that effect considerable cracking in order to secure the desired product antiknock quality by cracking out the poorer octane value components, such as normal paraflins, that are present in reformer feedstocks. In this manner, high antiknock levels can be reached but at the expense of liquid reformate yield and catalyst life.

In the prior art various proposals have been made of processes for producing gasoline blending stock involving combinations of a reforming step with a step for selectively removing normal parafiins (which latter step, for convenience, is referred to herein as denormalization). Usually the denormalization step involves the use of a molecular sieve adsorbent having pore diameters of about 5 angstrom units. Patents disclosing such combination processes include the following:

United States Pat. 2,886,508, H. V. Hess and E. R. Christensen, issued May 12, 1959, discloses a process in which the feed naphtha is first denormalized by means of molecular sieves and the denormalized feed is then reformed, for example, by means of a platinum-containing reforming catalyst in the presence of hydrogen at temperatures in the range of 750-975 F. and pressures in the range of 200700 p.s.i.g. The patent teaches that under these conditions the isoparaflinic constituents of the denormalized feed are substantially unaffected and the' resulting reformate is substantially free of straight chain hydrocarbons. It also teaches that straight chain hydrocarbons recovered from the absorbent can be upgraded by catalytic reforming or isomerization to yield additional gasoline blending stock.

Another patent to the same inventors, US. Pat. 3,007,- 863, issued Nov. 7, 1961, likewise describes a process involving denormalization of the feed naphtha followed by reforming. This patent also teaches that the use of a platinum-containing reforming catalyst at 750-975 F. and pressures of 200-700 p.s.i.g. does not substantially affect the isoparaffinic constituents of the denormalized feed and results in a reformate product which is substantially free of straight chain hydrocarbons.

Other references disclosing combination processes in which a naphtha fraction is first denormalized by means of molecular sieves and the denormalized naphtha is then catalytically reformed are the following United States patents: Pat. 2,945,804, C. E. Hemminger, issued July 19, 1960; Pat. 2,952,614, K. E. Draeger et al., issued Sept. 13, 1960; Pat. 2,958,645, C. N. Kimberlin, Jr. et al., issued Nov. 1, 1960; and Pat. 3,193,490, D. B. Boughton, issued July 6, 1965.

A reversed sequence of processing is described in another United States patent of the first-mentioned inventors, Pat. 2,917,449, E. R. Christensen and H. V. Hess, issued Dec. 15, 1959, wherein the process involves first reforming a naphtha containing straight chain hydrocarbons under relatively mild conditions to avoid cracking and thereafter denormalizing the reformate by means of molecular sieves. The patentees teach that by operating in this manner the life of the reforming catalyst can be extended for an indefinite period of time.

US. Pat. 2,958,644, C. N. Kimberlin, Jr. et al., issued Nov. 1, 1960, also describes a process utilizing the lastmentioned sequence of steps. This patent teaches that the feed naphtha is first reformed under condtions to produce a C hydroformate having a research clear octane number (F-l) of at least 90, after which the hydroformate is denormalized by means of molecular sieves to give a product of 100+ research clear octane number.

Other United States patents which disclose combination processes likewise involving a reforming step followed by denormalization of the reformate via molecular sieves include the following: Pat. No. 2,818,449, E. R. Christensen et al., issued Dec. 31, 1957; Pat. 2,818,455, W. P. Ballard et al., issued Dec. 31, 1957; Pat. 2,888,394, E. R. Christensen et al., issued May 26, 1959; Pat. 2,891,902, H. V. Hess et al., issued June 23, 1959; Pat. 2,944,001, C. N. Kimberlin, Jr. et al., issued July 5, 1960; Pat 3,081,255, H. V. Hess et al., issued Mar. 12, 1963; and Pat. 3,085,972, H. G. Krane et al., issued Apr. 16, 1963.

SUMMARY OF THE INVENTION The present invention provides an improved combination process involving reforming and denormalization steps, in which the sequence of steps is as follows: (1) denormalization of the naphtha feed; (2) hydroforming of the denormalized naphtha by means of a platinum-containing reforming catalyst under conditions, including temperatures of 750-975 F. and pressures above 125 p.s.i.g. such as 200-700 p.s.i.g., which give a C reformate having F-l clear octane number of at least 96 and preferably at least 98; and (3) denormalization of the resulting hydroformate to yield a C product having F-l clear octane number above 100 and preferably at least 102.

We have now discovered that when a naphtha feed comprising naphthenes, normal parafiins and branched paraffins including singly branched paraflins of the C -C range is first treated to remove the n-paraffins and the resulting denormalized naphtha is then subjected to reforming in the presence of hydrogen and a platinumcontaining reforming catalyst at temperatures and pressures as above stated, n-paraffins are formed during the hydroforming reaction and the amount thereof in the resulting reformate product is enough to significantly reduce its antiknock value. This is contrary to the teaching of the prior art as mentioned above. Also the total amount of singly branched paraffins of the C -C range in the product will be substantially less than when the same naphtha feed, without denormalization, is reformed under the same conditions. This is also believed to be true for singly branched paraflins of the C -C range if the feed naphtha boils high enough to include such isoparaflins, although analytical complications for such higher boiling range makes this difficult to determine. In any event, when the reformate produced from the denormalized naphtha is then treated to remove the n-paraffins in accordance with the present invention, a gasoline blending stock of superior antiknock quality is obtained, not only because the deleterious effect of the unexpected n-paraffins have been eliminated but also because there is an abnormally low content of singly branched paraffins of the C -C range and perhaps also of the C -C range. These singly branched paraffins have low antiknock values, so that the reduction in content thereof in the product is highly beneficial. For example, the methylheptanes with the methyl substituent at the 2-, 3- and 4-positions have F-l clear octane numbers, respectively, of 21.7, 26.8 andv 26.7. The present invention permits a significant reduction in the total content of these singly branched isoparaffins of the C -C range or higher. This reduction would not occur to comparable extent by reforming at given reforming conditions but without prior denormalization of the feed.

The effects of denormalizing the reformer feed are thus to permit a substantial reduction in the total C -C singly branched paraffins while unexpectedly producing straight chain paraffins which thereafter can readily be removed in a second denormalization step. Preferably the n-paraffins recovered from the two denormalization steps are combined and hydroformed under conditions to effect dehydrocyclization and yield a further amount of gasoline blending stock of high antiknock value.

The present process is advantageous in the preparation of gasoline blending stocks having F-l clear octane numbers above and particularly stocks of 102 or higher F-l value. The process is especially beneficial where reformates of unusually high antiknock values, such as 102110 F-l clear, are desired, since distinctly better yield-octane value relationships are secured than when denormalization, either before or after the reforming step, is omitted from the processing sequence.

BRIEF DESCRIPTION OF DRAWINGS The invention is described in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic illustration depicting the sequence of steps in the process;

FIG. 2 is a schematic flowsheet illustrating in more detail an embodiment of the invention; and

FIG. 3 is a graph showing the yield-octane number relationship for products obtained by four different processing procedures including that of the invention and three prior art procedures.

DESCRIPTION With reference first to FIG. 1, the feed material is a naphtha boiling in the gasoline range composed of hydrocarbons of different types comprising naphthenes, nparatfins and branched paraffins including singly branched paraffins of C C and optionally up to and including about C Usually the feed will also contain aromatic hydrocarbons, although dearomatized naphthas can, if desired, be used as charge to the process. The feed can be a wide gasoline fraction containing, for example, paraffins from C through C or it can be a narrow fraction within this range such as a fraction containing C C or C -C parafiins including singly branched parafiins.

This feed is first subjected to treatment, designated as denormalization step 10, adapted to remove the straight chain hydrocarbon components. These may include straight chain olefins and acetylenic components as well as the n-paraffins. Any procedure which will selectively remove straight chain hydrocarbons from the feed can be used in step 10. Procedures for effecting this type of separation are known in the art. A preferred type of procedure comprises selective separation of the straight chain hydrocarbons by means of a suitable adsorbent such as crystalline zeolite molecular sieves having pore diameters of about 5 angstrom units. Separations achieved in this manner are described in the various prior art patents referred to above. Another type of procedure that can be used is selective adduction of the n-paraffins with urea. Separations based on such adduction are discussed in the book New Chemical Engineering Separation Techniques, pages 282-288, Interscience Publishers (1962), and a process utilizing this technique, known as the Nurex Process, is described in Oil and Gas Journal, vol. 67, No. 33, p. 76 (Aug. 8, 1969).

The denormalized naphtha resulting from step 10, which is essentially free of straight chain hydrocarbons is then hydroformed in step 11. The hydroforming reaction is carried out in the presence of hydrogen and a platinumcontaining reforming catalyst under reforming conditions including temperatures in the range of 750975 F. (399- 524 C.) and pressures above p.s.i.g. and usually in the range of 200-700 p.s.i.g. Under these conditions naphthenes in the denormalized feed are converted to aromatics, singly branched paraffins of the C -C range or higher disappear to substantial extent and a significant proportion of n-paraffins are formed. Reforming conditions maintained in step 11 are such that the O reformate which results has an F-l clear octane number of at least 96, more preferably, at least 98.

The reformate from step 11 is then treated in a second denormalization step 12 which can be carried out utilizing the same type of separation technique as employed in step 10. Preferably this separation is accomplished by utilizing a molecular sieve adsorbent as described in the afore mentioned patents. The resulting denormalized reformate product, indicated at 13, is a high quality gasoline blending stock having F-l clear octane rating above 100. Typically the process is capable of producing in good yield gasoline blending stock having F-l clear octane numbers above 102, for example, in the range of 104-110, by virtue of the circumstances that the product is free of nparaflins and has an inordinately low content of singly branched parafiins of the C -C or higher range. The octane level reached will depend mainly on severity of the reaction conditions utilized in the reforming step.

The n-parafiins recovered from steps 10 and 12 preferably are combined, as indicated by lines 14 and 15, and then are reformed in a separate step 16 under dehydrocyclization conditions to convert same largely to aromatic hydrocarbons. The resulting dehydrocyclizate product optionally can then be blended with gasoline blending stock 13 to give an increased amount of high antiknock quality product.

FIG. 2 schematically illustrates a preferred manner of practicing the invention in which the removal of straight chain hydrocarbons from the feed to each of the denormalization steps is effected by selective adsorption utilizing zeolitic molecular sieves having pore diameters of about angstrom units. The naphtha feed, which enters the system via line 20, comprises naphthenes, n-paraffins and branched parafiins including singly branched parafiins of the C -C range or higher, and it may also contain other components such as straight chain and branched olefins and aromatic hydrocarbons. The feed can be a wide boiling or narrow boiling fraction and may, for example, have an initial boiling point in the range of 50- 200 F. (.10-149 C.) and an endpoint in the range of 260-475 F. (127-246 C.) The n-paraflin content of the feed can vary widely, e.g. 350% by weight, as also can the content of C -C or higher singly branched paraffins. The feed can be straight run naphtha, catalytically cracked naphtha, thermally cracked or reformed naphtha, hydrocracked naphtha, coker naphtha, Udex rafiinate or mixtures of such refinery stocks.

In the embodiment illustrated in FIG. 2, the feed naphtha preferably is vaporized in heater 21 and is passed through line 23 as a vapor into adsorber 24. The adsorber contains a bed of molecular sieve adsorbent, such as zeolitic calcium aluminosilicate, having uniform pore diameter of about 5 angstrom units. Such adsorbents are described in the various patents mentioned above, see, for example, U.S. Pat. 3,193,490. The temperature in the adsorbent can be in the range of 300-800 F. (149-427 C.), more preferably 350-750 F. (177399 C.), and is sufficiently high to maintain the naphtha as a Vapor at the prevailing pressure but not so high as to cause cracking. Contact of the hydrocarbon vapors with the adsorbent removes the straight chain hydrocarbons by trapping same in the adsorbent pores while allowing the branched and cyclic components to pass through the adsorbent bed and out of adsorber 24 via line 25.

While FIG. 2 shows only one adsorber 24, in practice a plurality of adsorber beds normally would be used in parallel so that the naphtha could be fed alternately to the beds in timed sequence to permit continuous introduction of naphtha to the system. Each bed would operate on a time cycle involving stages of adsorption of the straight chain hydrocarbons from the feed and desorption of the adsorbate from the molecular sieves. This adsorption-desorption operation could, if desired, be carried out by liquid phase contact of the feed naphtha and desorbing medium with the beds of molecular sieves, but vapor phase contacting is preferred and is utilized in the embodiment illustrated in FIG. 2. In each adsorption stage of a cycle the amount of naphtha fed to the bed would depend upon the straight chain hydrocarbon content of the feed and would not exceed the amount which would saturate the pores of the adsorbent with these components. The desorption stage preferably is carried out by utilizing hydrogen recycle gas from a dehydrocyclizing step hereinafter described, employing temperatures within the same range as above specified for the adsorption stage.

The denormalized naphtha withdrawn from adsorber 24 as a vapor through line 25 preferably is passed directly to heater 26 wherein it is heated to a suitable reforming temperature, after which it is subjected to hydroforming as indicated by reformer 27. As previously stated, the reforming reaction is carried out by means of a platinumcontaining reforming catalyst in the presence of hydrogen at suitable reforming temperatures in the range of 750- 975 F. and pressures of from or 200 p.s.i.g. to 700 p.s.i.g. A space velocity generally in the range of 0.5- 20 liquid volumes per hour per volume of catalyst (v./hr./ v.) and usually of 2 or more, e.g. 3 v./hr./v., is utilized. Average temperatures in the reformer 27 may be, for eX- ample, 875 F., 900 F., 925 F. or any value in the range of 875975 F. A plurality of reactors in series generally is used in this type of operation, with heaters between reactors for reheating the hydrocarbon reactants to com pensate for reductions in temperature that occur due to the endothermic reactions which take place. Under these reforming conditions naphthenes dehydrogenate to aromatics, a significant portion of the C -C or higher singly branched paraffins disappear by being converted to other components, and n-parafiins are formed in substantial amount. As a result of these reactions a reformate is produced which, on a (3 reformate basis, has an F-l clear octane number of at least 96. Preferably, the reforming conditions are selected to yield a C reformate having F-l clear octane number of 98 or higher. The octane level reached is controlled by the severity of the reforming conditions utilized in reformer 27 The effluent from reformer 27 is withdrawn through cooler 28 and passes to gas-liquid separator 29. The hydrOgen-containing gas phase is recycled from the top of separator 29 through line 30 and heater 26 back to reformer 27, while excess hydrogen is removed as indicated by line 31. A hydrogen recycle rate typically in the range of 3000-9000 s.c.f./bbl. of reformer feed is used and the hydrogen content of the recycle stream is generally in the range of 6098% by volume.

Any of the known or conventional platinum-containing reforming catalysts can be used for effecting the hydroforming reaction in reformer 27. Such catalysts have been described in numerous prior art references and need not be described herein. Reference can be made, for example, to the following: Catalytic Processes and Proven Catalysts by C. L. Thomas, pages 5457, Academic Press (1970); U.S. Pat. 2,479,109, V. Haensel, issued Aug. 16, 1949; and U.S. Pat. 2,478,916, V. Haensel et al., issued Aug. 16, 1949. The platinum-containing catalyst can also contain other metals, such as rhenium, ruthenium, rhodium or iridium, which are beneficial. The platinum-rhenium reforming catalysts are particularly desirable and such catalysts have been described in U.S. Pat. 3,415,737, H. E. Kluksdahl, issued Dec. 10, 1968, and U.S. Pat. 3,434,960, R. L. Jacobson, issued Mar. 25, 1969. Platinum-iridium reforming catalysts are disclosed in U.S. Pat. 3,554,902, W. C. Buss, issued Jan. 12, 1971.

The liquid reformate which passes from the bottom of separator 29 through line 32 contains a significant amount of n-paraffins but is substantially depleted of singly branched paraffins of the C C range or higher as compared to the charge to reformer 27 or as compared to reformate obtained for the same reforming conditions but without prior denormalization of the feed. This reformate is then treated in adsorber 33 to selectively remove the n-paraflin components. Preferably, the reformate is admixed with other reformate material from line 34, which is derived as hereinafter described and also contains nparatfins, and the mixture is then vaporized in heater 35 and fed through line 36 into adsorber 33. The latter also contains molecular sieves having about angstrom pore diameters and is operated in essentially the same manner as adsorber 24. Again a plurality of adsorber beds arranged in parallel preferably are used and are operated on a timed sequence of adsorption-desorption to permit continuous denormalization of the mixed reformate stream from line 36. The temperature in the adsorbent beds during both the adsorption and desorption cycles is maintained in the range of 300800 F. (l49-427 C.), more preferably 350-750 F. (177399 C.), and is high enough so that the hydrocarbon mixture contacting the adsorbent will be in vapor phase. This contacting causes the straight chain hydrocarbons to be retained in the pores of the molecular sieves but allows the other hydrocarbons to pass through the bed and out of the adsorption zone via line 37. During the adsorption phase of each cycle the amount of reformate fed to the adsorbent bed is not greater than the amount that will saturate the bed with n-parafiins, so that efiluent product obtained from line 37 will be substantially completely denormalized. This prod uct will constitute a high quality gasoline blending stock having F-l clear octane number above 100 and typically can have an F-l clear value above 102. Octane levels in the range of 104-110 can be reached, depending largely upon the severity of the reaction conditions in reformer 27.

Referring back to adsorber 24, after the adsorption stage of a cycle each bed is treated to strip from the adsorbent the n-parafiins and any other straight chain hydrocarbons therein adsorbed. This is done in the embodiment of FIG. 2 by contacting the adsorbent with hydrogen stripping gas which is a hydrogen recycle stream supplied through lines 38 and 39. The hydrogen recycle gas at a temperature in the range of 300-800 F. (149- 427 C.), more preferably 350-750 F. (177399 C.), is passed upwardly through adsorber 24 in amount effective for desorbing or displacing all of the straight chain hydrocarbons and removing them from the adsorption zone. The hot efiiuent composed of hydrogen recycle gas and straight chain hydrocarbons issues from the top of adsorber 24 through line 40.

Each bed constituting adsorber 33 is likewise desorbed in the same manner as adsorber 24. A stream of hydrogen recycle gas from line 38 and 41 is introduced into the bottom of the bed and flows upwardly in contact with the molecular sieve adsorbent at 300-800 F. (149427 C.), more preferably 350750 F. (177399 C.), to displace the n-paraffins. The hot effiuent issues through line 42 and passes to line 40 where it joins the hot efliuent from adsorber 24. The mixed stream, comprising straight chain hydrocarbons recovered from both the naphtha feed and the reformate from reformer 27, then is sent directly and without prior separation of any component through line 43 and heater 44 to a second reformer designated as dehydrocyclizer 45. This procedure is advantageous in that it avoids the loss of heat and cost of additional equipment that would otherwise be incurred if the straight chain hydrocarbons were first condensed and separated from the hydrogen recycle gas. Furthermore, since hydrogen recycle to the dehydrocyclizer 45 is required in any event, the use of hydrogen produced in this operation as the desorbing or displacing agent in both adsorber 24 and 33 and the return of the hot hydrogen, without any intermediate cooling, to dehydrocyclizer 45 effect distinct economies in the system.

The dehydrocyclization reaction in hydroformer 45 is carried out by any suitable reforming catalyst, such as a chromia-alumina catalyst, a molybdena-alumina catalyst, or platinum-containing reforming catalyst as referred to with reference to the operation of reformer 27. As a general rule, the temperature level is somewhat higher and the pressure somewhat lower for the dehydrocyclization step than for the reforming step in 27. Inlet temperatures to dehydrocyclizer 45 generally are in the range of 900-1000 F. (482538 C.) and more preferably 925-975 F. (496-524 C.), while the pressure generally is below 500 p.s.i.g. and usually falls within the range of 50250 p.s.i.g. Suitable reforming conditions for dehydrocyclizing straight chain hydrocarbons are described in several of the patents referred to above, e.g. US. Pat. 2,886,508, H. V. 'Hess et 211., issued May 12, 1959; also see U.S. Pat. 2,944,001, C. N. Kimberlin, Jr. et 211., issued July 5, 1960. Under the dehydrocyclizing conditions maintained in hydroformer 45 the straight chain hydrocarbons undergo dehydrogenation and cyclization, as a result of which a reformate or dehydrocyclizate product which is highly aromatic is obtained.

The efiluent from dehydrocyclizer 45 passes through cooler 46 into separator 47. Hydrogen recycle gas is withdrawn from the top of the separator, flows through line 48 to heater 49 where it is heated to the desired temperature for use as a desorption medium and then is recycled through line 38 for use in adsorbers 24 and 33. Excess hydrogen produced in dehydrocyclizer 45 is withdrawn from the system via line 50. The aromatic reformate or dehydrocyclizate removed from the bottom of separator 47 through line 51 can, if desired, be sent directly to gasoline blending as indicated by dashed line 52. However, since this reformate usually contains some straight chain hydrocarbons due to incomplete conversion in dehydrocyclizer 45, it is preferred to send it through line 34 and treat the same, along with the reformate from line 32, in adsorber 33 to effect removal of the straight chain hydrocarbons. By operating in this manner substantially all of the straight chain hydrocarbons either present in the feed naphtha to line 20 or formed during the reaction in reformer 27 are converted to other hydrocarbons.

The process above described with reference to FIG. 2 results in the conversion of the naphtha feed in good yield into a high quality reformate which is substantially free of n-paraffins and other straight chain hydrocarbons and which has an unusually low content of singly branched paraffins of the C -C or higher range. This product has Fl clear octane rating above 100, and the process more preferably is operated to yield product having F1 clear values in the range of 102-107 or even higher. The process provides distinct advantages with respect to product yields for such high octane levels, as compared to prior art processing procedures. These advantages are discussed hereinafter in conjunction with FIG. 3.

For purpose of illustrating the advantages of the invention, data were obtained for each of four procedures designed herein as A, B, C and D. Procedures A, B and C represent prior art processing sequences while Procedure D represents the process of the invention. In each case the starting material was a straight run naphtha having an A.S.T.M. boiling range of about 240320 F. (116l60 C.), A.P.I. gravity of 56, n-parafiin content of about 26% by weight, and sulfur and nitrogen contents of 1 and 2 p.p.m., respectively. Also, in each case the catalyst used in the reforming step was a commercial platinum-rhenium reforming catalyst comprising about 0.35% of each metal on eta alumina and also containing about 1% combined chlorine.

Each procedure comprised a reforming step utilizing the above-described catalyst and operated at approximately the following conditions: 350 p.s.i.g. pressure; H recycle rate=7400 s.c.f./bbl.; space velocity=2.02.1 v./hr./v.; mole ratio of H to oil=6.07.6. The reforming step in each case was operated in an isothermal reactor under these conditions and at several selected temperatures within the range of 875975 F. in order to vary reaction severity. Procedures B, C and D included a step for dehydrocyclizing n-parafiins recovered from the molecular sieves, in which step the same catalyst was used as in the reforming step. When a denormalization step was used, it was effected by means of 5 A. molecular sieves with the hydrocarbon material in liquid phase. Specifically, the sequences of steps and other conditions in the four procedures were as follows:

Procedure A.-Reforming only; conditions as above specified.

Procedure B.Reforming as above specified; denormalization of reformate; dehydrocyclization of resulting nparaflins 'at 925 F. (496 C.), 200 p.s.i.g., H recycle=7800 s.c.f./bbl., LHSV=2.2 v./hr./v. and H :oil mole ratio-=75; recovery and recycle to extinction of all n-paraffins in dehydrocyclizate. Product: a mixture of denormalized reformate and denormalized dehydrocyclizate.

Procedure C.--Denormalization of naphtha; reforming denormalized naphtha as above specified; dehydrocyclization of n-paraflins as in B except at 965 F. (518 C.). Product: a mixture of reformate from denormalized naphtha and dehydrocyclizate.

Procedure D.--Denormalization of naphtha; reforming denormalized naphtha as above specified; denormalization of reformate; dehydrocyclization of n-parafiins from naphtha and from reformate; recovery and recycle to extincition of all n-paraflins in dehydrocyclizate. Product: a mixture of denormalized reformate from denormalized naphtha and denormalized dehydrocyclizate.

From the foregoing summaries it can be seen that Procedure A is merely conventional reforming, Procedure D constitutes the process of the present invention, and Procedures B and C are essentially the processes, respectively, of US. :Pats. 2,968,644 and 2,886,508 referred to hereinbefore.

Table I shows the yields of C product corresponding to three levels of octane values obtained for each of the four procedures. Specifically, yields for F-l clear octane levels of 100, 103 and 106 are listed, along with the approximate reforming temperature required to secure these octane values.

TABLE I.--OCTANE-YIELD RELATIONSHIP FOR PROCE- DURES A-D The data in Table I show that one of the advantages of the present invention (Procedure D) is that the reforming step can be operated at a lower temperature than prior art Procedures A, B or C to obtain any given octane level product. Even more important, however, is the benefit provided by the invention with respect to yield-octane relationship for securing high octane value products. FIG. 3, based upon the data of Table I, clearly illustrates this benefit. Reference to FIG. 3 shows that Procedure B can provide an advantage in octane-yield relationship as compared to conventional reforming (Procedure A) and Procedure C can also provide an advantage at octane levels above 102, but that the process of the present invention (Procedure D) will give the greatest advantage of all. This advantage can readily be seen from the curves shown in FIG. 3, which indicate that the yieldoctane relationship advantage provided by Procedure D generally becomes progressively greater as higher octane levels above 100 are reached.

Reformates produced in the foregoing procedures, when employing a reforming temperature of about 925 F. (496 C.) and other reforming conditions as described, were analyzed through the C range and the contents of TABLE IL-Cs-Co PARAFFIN ANALYSES Weight percent in material analyzed Total C0-C9 Total C5-C9 normal singly branched paratfins paraflins Material analyzed Untreated feed naphtha 0 reformates from Procedure' A 3.3 9.6 B- 0 9.9 C- 2.6 6.7 D 0 6.9

From Table II it can be seen that all of Procedures A through D result in reformates with reduced amounts of singly branched paraffins as well as normal parafiins. However it can also be seen that only the reformate produced by the present procedure (D) is free of normal 'parafiins while also having an unusually low content of the singly branched paraflins. The product of Procedure C (denormalization followed by reforming) also has an unusually low content of the singly branched parafiins but the normal paraffins, which appear therein unexpectedly, are quite detrimental with respect to antiknock value. While the contents of these normal parafiin and singly branched paraffin components in the C reformates do not appear large in any event, the amounts involved are quite significant, in view of the poor octane values possessed by both of these types of paraflins as compared with the high octane values desired for the products.

The invention claimed is:

1. Process for preparing a gasoline blending stock having F-l clear octane number above from a hydrocarbon feed of the gasoline boiling range composed of hydrocarbons of different types comprising naphthenes, n-paraflfins and branched paraffins including singly branched paraffins of the C -C range, which comprises:

(a) treating said hydrocarbon feed to selectively remove the n-paraffins and yield a fraction substan tially free of n-paraffins and containing naphthenes and branched parafins including singly branched parafiins of the C 0 range;

(b) reforming said fraction in the presence of hydrogen and a platinum-containing reforming catalyst under reforming conditions that result in a (3 reformate having F-l clear octane number of at least 96, said conditions including temperature in the range of 750-975 F. and pressures in the range of l25700 p.s.i.g., whereby said reforming effects dehydrogenation of naphthenes to aromatics, reduces the content of the C -C singly branched paraifins and effects substantial formation of n-paraffins, to yield a reformate having substantial n-parafiin content and a lower content of C -C singly branched paraffins than would be obtained by omitting Step (a);

(c) and treating the reformate to selectively remove n-paraffins therefrom and yield a gasoline blending stock having F-l clear octane number above 100.

2. Process according to claim 1 wherein said treating in each of Steps (a) and (c) to selectively remove the nparaifins is effected by means of molecular sieves having pore diameters of about 5 angstrom units.

3. Process according to claim 2 wherein said reforming conditions in Step (b) result in a C reformate having F-l clear octane number of at least 98 and said gasoline blending stock from Step (c) has an F-l clear octane number of at least 102.

4. Process according to claim 2 wherein n-parafiins selectively removed in Steps (a) and (c) are subjected to separate reforming (cl) under catalytic dehydrocyclizing conditions to remove hydrogen therefrom and produce 1 1 an aromatic dehydrocyclizate containing a minor proportion of n-paraflins, said removed hydrogen is utilized as hydrogen recycle gas to reforming Step ((1), and (e) said dehydrocyclizate is treated to remove the normal paraflins therefrom.

5. Process according to claim 4 wherein the treatment of said dehydrocyclizate to remove nparatfins is effected by introducing said dehydrocyclizate to Step (c).

6. Process according to claim 4 wherein Steps (a) and (c) are carried out by contacting the respective feeds thereto in vapor phase with said molecular sieves at 350- 750 F. to selectively absorb normal paraffins, the molecular sieves are then contacted at 350750 F. with hydrogen recycle gas derived from said reforming Step ((1) to displace n-paraffins, and the resulting etfiuent mixture of n-parafiins and hydrogen recycle gas is passed directly to the reforming Step ((1) without prior separation of any component.

7. Process according to claim 6 wherein the treatment of said dehydrocyclizate to remove n-parafiins is effected by introducing said dehydrocyclizate to Step (c).

8. Process according to claim 4 wherein said reforming conditions in Step (b) result in a C reformate having F-l clear octane number of at least 98, and wherein said gasoline blending stock comprises a mixture of denormalized reformate from Step (c) and denormalized dehydrocyclizate from Step (e), said mixture having an F-l clear octane number in the range of 102-110.

9. Process according to claim 1 wherein said pressure is in the range of 200-700 p.s.i.g.

10. Process according to claim 9 wherein said reforming conditions include temperature in the range of 875- 975 F.

11. Process for preparing a gasoline blending stock having F-1 clear octane number above 100 from a hydrocarbon feed of the gasoline boiling range composed of hydrocarbons of different types comprising naphthenes, n-parafiins and branched parafiins including singly branched parafiins of the C -C range, which comprises:

(a) contacting said hydrocarbon feed in vapor phase with molecular sieves having pore diameters of about 5 angstrom units to selectively absorb n-parafiins and yield a fraition substantially free of n-paraflins and containing naphthenes and branched parafiins including singly branched paraffins of the C -C range; (b) reforming said fraction in the presence of hydrogen and a platinum-containing reforming catalyst under reforming conditions that result in a C reformate having F-1 clear octane number of at least 96, said conditions including temperature in the range of 750975 F., pressure in the range of 125-700 p.s.i.g. and space velocity in the range of 0.5-2.0 v./hr./v., whereby said reforming effects dehydro- 12 genation of naphthenes to aromatics, reduces the content of the C -C singly branched parafiins and effects substantial formation of n-parafiins, to yield a reformate having substantial n-paraffin content and a lower-content of C -C singly branched paratfins than would be obtained by omitting Step (a);

(c) contacting the reformate in vapor phase with molecular sieves having pore diameters of about 5 angstrom units to selectively remove n-parafiins therefrom and yield a gasoline blending stock having F-1 clear octane number above 100;

(d) desorbing n-parafiins from the molecular sieves specified in Steps (a) and (c) by means of a gaseous displacing agent as hereinafter specified to yield vapor phase streams composed of n-paraflins and said displacing agent;

(e) feeding said streams directly without prior separation of any component to a separate reforming zone and therein subjecting the n-paraffins to catalytic dehydrocyclizing conditions to effect conversion thereof to aromatics; (f) cooling and separating the effiuent from said reforming zone to yield an aromatic dehydrocyclizate containing a minor proportion of n-paraffins and to recover hydrogen recycle gas;

(g) vaporizing said dehydrocyclizate and introducing the vapors to Step (c) to separate n-paraflins therefrom;

(h) and utilizing hydrogen recycle gas from Step (f) as said gaseous displacing agent.

12. Process according to claim 11 wherein said reforming conditions in Step (b) result in a C reformate having F-l clear octane number above 100, and said gasoline blending stock from Step (c) is a denormalized mixture of said reformate and said dehydrocyclizate, said mixture having an F-l clear octane number in the range of 102-110.

13. Process according to claim 11 wherein said pressure is in the range of 200-700 p.s.i.g.

14. Process according to claim 13 wherein said reforming conditions include temperature in the range of 875-975 F.

References Cited UNITED STATES PATENTS 7/1960 Kimberlin et al. 260-676 MS 9/ 1960 Draeger et al 208-79 US. Cl. X.R. 

